Geodesy

GOCE first geoid

Geodesy is concerned with the measurement of Earth's shape and the mapping of its regions. Geodetic products are used extensively in all branches of the Earth science. They are also used in areas of civil engineering, exploration, mapping and cadastral work, and are the basis of all geo-information systems.

Whereas positioning on Earth's surface in two- or three-dimensional coordinates is based on purely geometric techniques, height determination requires knowledge of Earth’s gravity field. Only through knowledge of differences in gravity potential is it possible to decide on the direction of the flow of water or the direction of 'up' and 'down'.

Since it represents a surface along which no water would flow, the geoid defines our sense of the horizontal and is the classical reference surface for establishing height. However, there is currently no globally unified height-reference system. There are numerous practical implications of having any number of nationally accepted benchmark references, such as how to define the true height of a mountain.

Levelling

Data from GOCE will lead to a global unification of height systems, so that mountain ranges in American can be measured against those in Europe or Asia. In the construction industry, an accurate geoid will be used for levelling to ensure, for example, that water flows in the direction intended.

GOCE data will also aid the building of bridges over water and tunnels through mountains – especially those linking different countries currently using different reference benchmarks. This issue was illustrated in the 1990s with the construction of the Øresund Bridge, which now links Denmark and Sweden. Much effort was taken in connecting two national height systems and precise levelling over the 22 km span of the bridge.

GOCE data will also facilitate one global system for tide-gauge records, so that sea levels can be compared all over the world. This will also contribute to observing and understanding sea-level change as a result of melting continental ice-sheets associated with a changing climate and postglacial rebound.

The GOCE geoid will provide a global standard that will greatly simplify all these height-related issues.

Last update: 16 September 2010

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